Not in my experience. In fact, necklaces are weird. I just pulled one last night with a really big silver and gold cross. (haven't tested it yet, though it was ringing between silver and gold, as expected). What is weird about the necklaces, is that if they're thin, you'll get isolated signals that don't display/sound off like a normal target that is thick. In fact, if your necklace is unclasped and strung out, you can easily miss them if they're thin gold. It's weird that way. If you happen to catch the strand along the horizontal (swinging down the length), you'll get a solid signal and likely be fairly accurate on metal type. The moment you hit that sucker at a diagonal, or across the vertical, the signal bounces funny. In fact, the one I dug last night, I was convinced was a pocket spill, due to the crappy signals that were all over the place. It was "different" than anything I'd encountered (actually, only since the last necklace, LOL), and I definitely wanted to find out what it was. Goes back to "dig everything" of course.
The thicker the necklace strand, the easier it is to detect, but the composition of the metals will make every necklace display/sound off weird. Since gold, for example, isn't likely to come in 24K necklace (too soft), you'll get an alloy that will cause the signal to bounce erratically, depending on the content. They're all a bit different, in my experience, so there's no really good way to make the ID, other than to suggest "you'll get erratic signals, depending on direction of swing, and depth"
The best necklaces, of course, are the ones with a pendant of some sort on them. Those typically have a solid signal at some point, and the chain along the edge.
Last piece of advice. If you DO come across a signal that is strong in one area, and bounces in another, dig on the OPPOSITE side of the bounce. You'll be less likely to drive a digger tool through the chain, breaking it. I've used this advice 100% of the time, and have never broken a chain, yet (with 7 necklace finds this year).
Cheers!
Skippy